The phenomenon of cavitation, as it sometimes happens in pumps, is generally undesirable, as it can cause choking of the pump and sometimes considerable damage not only to the pump but also auxiliary equipment.
However, cavitation, more narrowly defined, has been put to use as a source of energy that can be imparted to liquids. Certain devices employ cavities deliberately machined into a rotor turning within a cylindrical housing leaving space for liquid to pass. A motor or other source of turning power is required as well as an external pump to force the fluid through. The phenomenon of cavitation in all previous devices relevant hereto is caused by the rapid passage of the liquid over the cavities, which creates a vacuum in them, tending to vaporize the liquid; the vacuum is immediately filled again by the liquid and created again by the movement of the liquid, causing extreme turbulence in the cavities, further causing heat energy to be imparted into the liquid. Liquids can be simultaneously heated and mixed efficiently with such a device. Also, although the cavitation technique is locally violent, the process is low-impact compared to centrifugal pumps and mixing pumps employing impellers, and therefore is far less likely to cause damage to sensitive polymers used in oilfield fluids. Centrifugal pumps tend also to break large particles such as drill cuttings into small, low gravity particles which are more difficult to separate by centrifugation. The impeller blades of many types of pumps will fracture and break solids into smaller particles which may resist separation by any conventional method.
Good mixing is especially important in mixing oil field fluids such as drilling fluids and fracturing fluids.
Proper operation of the cavitation device, until now, has generally required a separate pump. Liquid must be forced through the existing cavitation devices to accomplish substantial heating, mixing, or both. Cavitation devices are excellent for intimately mixing gases with liquids, but centrifugal pumps do not handle large volumes of gases well, sometimes losing the ability to pump at all when the gas volume s too great. A disc pump can easily handle and pump mixtures containing significant volumes of gas.
Moreover, in the conventional cavitation devices, there is a viscous or surface effect drag against the stationary end wall of the cavitation device housing. There is a need for improvements to overcome these disadvantages of the existing cavitation devices.